FOR 5726:  Density dependent symbiosis in planktonic systems – DynaSym

• Subject Area: Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 528028597

The consequences of species interactions for population and community dynamics are a cornerstone of ecological and evolutionary research. While almost all theory in ecology still builds on the notion that the form of species interactions, e.g., predator-prey or mutualistic relationships, is fixed, accumulating evidence suggests that it can depend on the prevailing environmental conditions and be mediated by altered population densities. Despite the consensus on such context-dependence of the form of species interactions, it is rarely integrated into general theories on the regulation of population dynamics, community structure and functioning, even though it is of utterly importance for predicting community responses to environmental change. The proposed research unit aims to fill this gap in current theory by integrating density-dependent symbiosis into existing theory of community ecology. We will combine new experimental and theoretical approaches and consider symbiotic relationships - that is, the close association between two different species or organismal groups living together - as a continuum of interactions which can change along a gradient of densities e.g., from mutualistic to parasitic. The central goals of the research unit are to identify density-dependent changes in the form of symbiosis and their consequences for population and community dynamics. The research unit subprojects will determine the density dependence of symbiotic interactions in different community modules by comparing costs and benefits of interacting species. By linking shifts in costs and benefits to the shape of functional and numerical responses of interacting partners, we will provide a process-based understanding of shifts in the form of symbiosis and their effects on population and community dynamics. Subsequently, we will explore the possibility of a feedback between density dependence of the form of symbiosis and population dynamics. Such feedback dynamics could lead to a continuous shift in the form of the symbiosis, for example a shift between competition and mutualism between phytoplankton and associated bacteria over time. The research group focuses on community modules in planktonic systems, which allow to develop general theory, pursuing an approach contributing to theory building in the field of community ecology at a larger scale. This integrative approach requires collaboration across the proposed subprojects in targeted experiments and modelling and will produce synergies and novel mechanistic insights into the regulation of communities. The research unit is uniquely positioned in this context by taking an interdisciplinary approach of collaborating experts in experimental ecology and evolution with modelers to capture the full picture of community dynamics and to advance a vibrant research field.

• DFG Programme: Research Units
• International Connection: Israel

Projects

• Context-dependent effects on protective symbiosis driven by predation, competition and parasitism (Applicant Weithoff, Guntram )
• Coordination Funds (Applicant Becks, Lutz )
• Density dependence of symbiont-mediated immunity and parasite epidemics in symbiont-protected host populations (Applicant Uecker, Hildegard )
• Density dependence of the symbiosis in ciliate-algae systems (Applicant Becks, Lutz )
• Shifts in bacteria-algae symbiotic interactions - effects on plankton community dynamics and properties (Applicant Matthiessen, Birte )
• Shifts in the form of a ciliate – microalgae symbiosis in response to altered prey densities, competitor densities and temperature (Applicants Klauschies, Toni ;  Moorthi, Stefanie )
• Synthesis of context-dependent form of symbiosis (Applicant Becks, Lutz )
• Towards a process-based understanding of context-dependent forms of symbioses (Applicants Gaedke, Ursula ;  Klauschies, Toni )
• Trait related direction of density dependent effects in freshwater host endosymbiont systems (TREND) (Applicants Stibor, Herwig ;  Stockenreiter, Maria )

• Spokesperson: Professor Dr. Lutz Becks